The present invention generally relates to a method and apparatus for applying terminals to the ends of wire and inspecting the quality of the termination automatically at or during the time of the termination application. More specifically, the present invention relates to a method of calibrating a crimping press such that during the application of a terminal to the end of a wire, the measured force profile curve can be compared to a predetermined ideal force profile curve for an acceptable termination.
In the art of wire processing, and more specifically in the process of applying terminals to the ends of wire, it is important that the process does not allow any undetected bad terminations between the applied terminal and the bare wire. The process of applying terminals and inspecting the quality of the termination automatically at or during the time of the terminal application is a desired feature that has been performed in many ways in prior art systems.
In the prior art systems, there are several methods of crimp quality monitoring (CQM). These methods range from the manual visual inspection of the termination by the operator and manual measurements of the termination height (crimp height), width, and pull force to the automated monitoring of the crimping forces and actual crimp height during the crimping process. The higher end and more sophisticated methods for CQM utilize a sensor in the crimping press unit/applicator to measure the force or strain exerted during the process. Typically, the sensor is a piezoelectric load sensor.
After completion of the crimping operation, the output of the piezoelectric load sensor is analyzed and compared to known profiles representing a satisfactory terminal application. As an example, U.S. Pat. No. 5,271,254, incorporated herein by reference, illustrates a CQM method in which the load sensor and an encoder are used to produce an actual crimping force envelope that includes a peak force value and the total work of the crimping press. The actual crimping force envelope is compared to an ideal envelope and a failure signal is generated if the actual envelope varies from the ideal.
Typically, the ideal force profile of an acceptable termination is learned into the CQM system at the beginning of the termination process by repeatedly compiling the force data over several cycles in which an acceptable termination is created. Once the ideal force profile has been determined, a control unit monitors for variations in the actual, measured profile as compared to the known ideal profile as terminals are applied to the ends of wire. If a significant variation is detected, the bad termination is discharged. If several consecutive bad terminations are detected, operation of the crimping press unit may be suspended until the problem has been identified.
Although this method of CQM is effective in identifying a bad termination, a drawback exists in that each time a new crimp height or a different type of wire or terminal is applied, the crimping press must go through a learning process to determine the ideal profile of an acceptable termination. In facilities that use a crimping press to run many small batches of wire terminations each utilizing different size wires and terminals, the process of learning the ideal profile for an acceptable termination creates a substantial hindrance.
Therefore, it is an object of the present invention to provide a method of calibrating a crimping press, such that after calibration, the force measurements taken during operation can be compared to a previously determined ideal profile curve and defects detected. It is an additional object of the present invention to provide a master tool and a common test bar to calibrate each individual crimping press. Further, it is an object of the present invention to provide a method that standardizes the piezoelectric load sensor contained in separate individual crimping presses such that the load sensor generates an output nearly identical to the output of similar load sensors in separate crimping presses.
The present invention is directed to a method and an apparatus for calibrating a crimping press such that during the application of a terminal to the end of a wire, the measured force profile curve can be compared to a predetermined standard force profile curve for a satisfactory termination.
Initially, a master tool is positioned in a test crimping press. The master tool includes a stationary anvil and a movable die member. The die member is mounted to a movable body of the master tool, which in turn is coupled to the movable ram contained in the test crimping press. As the crimping press moves the ram between its open and closed positions, the die member of the master tool moves toward and away from the stationary anvil.
A test bar having a standardized shape and composition is positioned in the master tool between the anvil and the die member. As the test crimping press moves to the closed position, the die member of the master tool crimps the test bar positioned in the master tool. After the test bar has been crimped, the crimp height of the test bar is measured and compared to a desired crimp height. If the measured crimp height does not equal the desired crimp height, the shut height of the test crimping press is adjusted and the crimping steps repeated until the measured crimp height equals the desired crimp height.
Once the measured crimp height equals the desired crimp height, the control unit for the test crimping press records the forces measured during operation of the test crimping press as a standard force profile curve. The standard force profile is recorded from a test load sensor positioned in the test crimping press that measures the amount of force applied by the test crimping press during the crimping of the test bar. The standard force profile determined by the test crimping press is recorded in the control unit such that the standard force profile can be used during the calibration of additional crimping presses.
After the standard force profile has been determined, the master tool is transferred to a crimping press that is being calibrated. Once the master tool has been installed in the crimping press, the control unit of the crimping press is set to its default, or xe2x80x9czeroxe2x80x9d shut height and the crimping press is operated to crimp the test bar between the die member and anvil of the master tool. The crimp height of the test bar is measured and the shut height of the crimping press being calibrated is repeatedly adjusted until the measured crimp height equals the desired crimp height.
During the repeated adjustments in the shut height of the crimping press to create the desired crimp height, the shut height of the crimping press is adjusted from its default or xe2x80x9czeroxe2x80x9d position by a shut height adjustment factor. Once the desired crimp height has been formed, the zero position of the crimping press is offset by the adjustment factor such that when the crimping press is subsequently set at the zero position, the crimping press being calibrated will produce the desired crimp height.
Once the shut height adjustment factor has been determined for the crimping press being calibrated, an actual force profile is recorded in the control unit of the crimping press being calibrated. The actual force profile is determined by measurements taken from a load sensor contained in the crimping press.
The actual force profile measured during the crimping of the test bar to the desired crimp height is compared to the standard force profile previously determined in the test crimping press. If the actual force profile varies from the test force profile, an offset factor is determined that, when applied to the actual force profile, adjusts the actual force profile such that the actual force profile replicates the standard force profile.
Once the offset factor and the shut height adjustment factor have been determined, the master tool is removed from the crimping press and the crimping press can be used to apply terminals to the ends of wire. The offset factor is utilized in combination with the output of the load sensor such that the output of the load sensor is standardized, while the shut height adjustment factor normalizes the zero position for each crimping press. Thus, ideal force profiles and ideal shut height adjustments from the zero position for the various terminal application processes can be input into the control unit of the crimping press and the output of the load sensor compared to the ideal force profile to determine whether a suitable terminal application has been performed. In this manner, a set of ideal force profiles can be input into the control unit without the requirement of the crimping press learning the ideal force profile for each variation in the process being performed.
Various other features, objects and advantages of the invention will be made apparent from the following description taken together with the drawings.